Harbin Engineering University

About: Harbin Engineering University is a education organization based out in Harbin, Heilongjiang, China. It is known for research contribution in the topics: Control theory & Microstructure. The organization has 31149 authors who have published 27940 publications receiving 276787 citations. The organization is also known as: HEU.

Electrochemical and Capacitance Properties of Rod-Shaped MnO2 for Supercapacitor

Abstract: A novel kind of electrode material, rod-shaped MnO 2 , was synthesized under high viscosity for the first time. The MnO 2 was proved to be the multicrystal with the mixture of α- and γ-MnO 2 by X-ray diffraction. From transmission electron micoscopy, it could be seen that the sample has a length of 250 ∼ 350 nm and a diameter of 10 ∼ 15 nm. The ratio of length to diameter could reach more than 20:1. The electrochemical properties were examined by cyclic voltammograms (CV), galvanostatic charge/ discharge, and electrochemical impedance spectroscopy (EIS) in three electrode cell. According to CV results, 2 mol L - 1 (NH 4 ) 2 SO 4 aqueous solution was a proper electrolyte for MnO 2 supercapacitors. A maximum specific capacitance (SC) of 398 F g - 1 was obtained from galvanostatic charge/discharge curve in 2 mol L - 1 (NH 4 ) 2 SO 4 solution at constant current of 10 mA. The SC value was 328 F g - 1 at a high current of 50 mA which exhibit high power characteristics of the rod-shaped MnO 2 . The electrolyte resistance was 0.21 Ω cm 2 by researching on EIS. Long cycle-life and high coulombic efficiency of rod-shaped MnO 2 were also demonstrated by charging and discharging 1000 cycles.

Graphene homogeneously anchored with Ni(OH)2 nanoparticles as advanced supercapacitor electrodes

Abstract: A green and facile approach was demonstrated to prepare graphene nanosheet/Ni(OH)2 (GNS/Ni(OH)2) composites for supercapacitor materials. GNSs as a support material can offer moderate active sites for the nucleation of Ni(OH)2, as well as an excellent electron transfer path. Then, ultrafine Ni(OH)2 nanoparticles were homogeneously anchored onto the surface of GNSs as spacers to ensure the high electrochemical utilization of the graphene layers and supply the open nano-channels for shortening the ion diffusion pathway. The results show that the GNS/Ni(OH)2 composites exhibit a superior specific capacitance of 1985.1 F g−1 and excellent cycle life with a loss of specific capacitance of only 6.5% after 500 cycles. The improved high electrochemical performance is attributed to the increased electrode conductivity in the presence of the graphene network and the increased effective interfacial area caused by the well-dispersed Ni(OH)2 on the GNSs.

Transportation theory of multiple scattering and its application to seismic coda waves of impulse source

Abstract: The energy distribution of elastic waves in an infinite elastic medium with uniformly and randomly distributed scatterers has been researched. The scattering process is assumed to be isotropic and without conversions between wave types. We get the equation on the distribution of energe density in time and space covering single as well as multiple scattering. Taking physical symmetry of the field into account, it can be simplified. In the case of small earthquakes, the energy source of elastic waves can be assumed as a short pulse emitted isotropically at t=0. The first-order approximate solution in the 3-dimensional space can be obtained, and it is equivalent to Sato's solution for single scattering. In the 2-dimensional space the complete analytical solution has been derived by the mathematical inductance which leads to a conclusion that the codas of surface waves can give the Q-factor related to intrinsic absorption. The equation obtained in this paper is more general.